R/eurusds.R

In szigony/xchangeR: xchangeR package for USD/EUR exchange rate

#' USD/EUR exchange rates
#'
#' Looks up the daily USD/EUR exchange rate via an API call for the specified date range.
#'
#' @export
#'
#' @importFrom httr GET content
#' @import dplyr
#' @importFrom data.table data.table as.data.table
#'
#' @param date_from The start of the range.
#' @param date_to The end of the range.
#' @param last_x_days Return the exchange rates for the last X days compared to \code{date_to}.
#'
#' @return Returns the daily exchange rates.
#'
#' @format Returns a \code{data.table}.
#' \itemize{
#'     \item \code{date}: The day for which the exchange rate was valid.
#'     \item \code{exchange_rate}: Daily exchange rate.
#' }
#'
#' @examples
#' # Specific date range
#' eurusds("2019-05-01", "2019-05-24")
#'
#' # Last 45 days from a specific date
#' eurusds(date_to = "2019-05-01", last_x_days = 45)
#'
#' # Last 45 days from today
#' eurusds(last_x_days = 45)
#'
#' @seealso \code{\link{eurusd}}

eurusds <- function(date_from, date_to, last_x_days = NULL) {
  if (is.null(last_x_days)) {
    date_from <- date_from
  } else {
    if (missing(date_to)) {
      date_to <- format(Sys.Date(), "%Y-%m-%d")
    }
    date_from <- format(as.Date(date_to, "%Y-%m-%d") - last_x_days, "%Y-%m-%d")
  }

  exchange_rates <- content(
    GET(
      "https://api.exchangeratesapi.io/history",
      query = list(
        base = "USD",
        symbols = "EUR",
        start_at = date_from,
        end_at = date_to
      )
    )
  )$rates

  eurusds <- data.table(
    date = as.Date(names(exchange_rates)),
    exchange_rate = as.numeric(unlist(exchange_rates))
  ) %>%
    arrange(date)

  return(as.data.table(eurusds))
}